Numerous methods and apparatus are known, widely available and commercially practiced for winding various materials about a spool, bobbin, or like core element. Such windings typically take the form of large rolls, e.g., as with carpeting and newsprint; as pancake coils, e.g., as with bow ribbon and reel-to-reel recording tape; or a helical or transverse winding, e.g., as with binding ribbon, cord, and prepreg slit tape. In the latter the winding is most often about spool or bobbin whose length is many times the width of the material being wound and the feed of material, as the winding progresses, moves from one end of the spindle to the other, back and forth, gradually building the layers of wound material about the spool or bobbin.
The aforementioned winding processes are typically performed by laying one layer atop another. However, not all materials are suitable for or amenable to winding of one layer atop another. Specifically, materials that are sticky, tacky, or adherent or are comprised of a flowable material, especially one that flows slowly over time, most especially at ambient and higher temperatures, are not amenable to being successively wound, one layer atop another as they may bind to one another or may manifest a tendency to morph into one another. Winding without a support also poses problems where the material being wound has poor physical integrity or strength and/or high flexural or elongation properties since too much tension in a winding process or, more so, in the unwinding process can cause a break in the material being wound or unwound, respectively.
To address these issues, it is common to employ a liner material which is inserted or interleafed between successive windings of the material being wound. The composition and physical properties of these liner materials are most often chosen to meet the needs of the specific winding process. For example, when one is winding a sticky, tacky and/or adherent material, it is most common to employ a liner that is or serves as a release liner whose composition is of a non-stick material and/or whose surface is treated with a release agent or coated with a release coating: the release properties of the liner, treatment or coating preventing the adherent from binding to the liner material itself. Where the material being wound is in need of structural support or strength, the liner may be a woven or non-woven fabric or fabric-like material or a high strength polymer film.
Apparatus for interleafing the liner materials are also well known, widely available and commercially used. Generally speaking, they integrate an unwinding station having a freely rotating axel and a plurality of feed and alignment guide elements into a standard winding apparatus. The axel is adapted to hold a pancake coil or spool of the liner material and the feed and alignment guide elements are configured to direct the liner material from the unwinding station to the winding station to be mated with the material being wound while concurrently aligning the strip of the liner material with the material being wound so that the two layers overlay one another at a point prior to that at which they make contact with the spool or winding. As noted, typically the axel upon which the spool of liner is mounted is freely rotating, i.e., its rotation is caused by the pull or draw of the liner material as it is wound with the first material, and is not motor driven. Given the speed with which certain of these winding apparatus operate, it is also common for the unwinding station to integrate or have associated therewith, especially with the axel, a means, element or component which places or creates a slight resistance in or to the rotation of the axel and/or the spool of liner material mounted thereon. The resistance is very low such that a minimum tension from the winding process enables the unwinding of the liner material but sufficient to prevent the axel from continuing to freely rotate with the concomitant unwinding of the liner material should the winding process be stopped suddenly.
Notwithstanding the foregoing, as much benefit as the resistance means provides in preventing the unrestrained unwinding in the case where the apparatus is suddenly stopped, it creates a new concern in the unwinding of liner itself. Specifically, as the spool of wound material grows and the spool of liner shrinks the speed of rotation of the axel holding the liner material becomes faster and faster. Here the resistance has the adverse effect of adding more and more tension to the liner material as the demand for liner is much more urgent as the supply dwindles on the axel. At a minimum this results in a stretching and/or twisting of the liner material, which, in turn leads to a narrowing of the width of the line material and/or greater difficulty in proper alignment of the liner material with the material being wound. At worst, it can lead to a break in the liner material necessitating the shut down of the process to re-feed the liner to the winding element. Slowing the overall winding process may help alleviate some of this concern, but any slow down in the winding process has an adverse economic effect on the efficiency of the overall production process.
Furthermore, while certain interleafing winding processes, e.g., those wherein the material being wound is structurally sound, stable, non-adhesive, non-tacky and non-flowing, may enable the use of liners whose width is the same as that of the material being wound, most interleafing or interlining processes, as they are also referred, employ, and must employ, a liner that is somewhat wider than the material being wound. This is especially true for those winding processes wherein the material being wound manifests a sticky, tacky or adhesive property material or involves a flowable material or a material that will or may manifest creep during winding, storage, handling and transportation, or any time prior to use and most especially those also involving a helical or transverse winding process. In the case of adherent, sticky or tacky materials, the wider tapes are necessary to address the lack of accuracy in being able to directly align the edges of the material being wound with the edges of the liner material, especially in higher speed winding processes, as well as those situations wherein the liner is narrowed owing to increased tension in the liner as it is being unwound. In the case of those wound materials that are subject to flow or creep, a wider liner prevents the materials from flowing past the edges of the liner to bind and/or morph with underlying layers and or adjacent windings.
Regardless, whether the process involves one or the other or both of the foregoing issues, the ultimate effect is an adverse impact on processing speed and utility of the final product. Specifically, if one must adjust the winding speed to address the deficiencies in the overall winding process or eliminate or reduce out-of-specification products, the overall efficiency and costs are adversely impacted. Similarly, if the material being wound binds or morphs with underlying layers or adjacent windings, one has a strong potential for significant irregularities in the unwinding process or a loss of the whole of the winding itself. For example, if one layer or winding binds to or morphs with another, then as that layer is being unwound, it will tend to tear the winding to which it is bound or morphed or simply fail to unwind. In the former, the whole or a significant part of that wound material is useless. In the latter, the inability to unwind may lead to a total shut down of the manufacturing process in which the wound material is being used. Of course not all situations will lead to as catastrophic scenarios as presented in the foregoing; however, even a seemingly minor snag or catch caused by one winding being slightly bound or tacked to another may alter the dimensions or create a defect in the material being unwound, adversely affect the physical properties of the ultimate end products being made from the wound material or trigger sensors that monitor changes in the tension of the material as it is unwound which, in turn, may lead to a shut down the process to allow for an inspection of the material to ensure its integrity and in-specification characteristics.
While many improvements and advancements in winding and unwinding processes have been made, there is still a need for an interleafing process which provides for a constant or substantially constant tension in the liner material as it is being wound, irrespective of the line speed.
Additionally, there is a need for an interleafing process which allows for even higher speed windings with greater accuracy in the alignment of the liner to the material being wound, especially in the winding of adhesive, sticky, tacky, and/or flowable materials.
Finally, there is a need for a high speed interleafing winding process which allows for liner widths that are the same as or essentially the same as that of the material being wound, even when winding flowable and/or adherent, tacky or sticky materials.